Crimson-colored pigment composition and the utilization thereof

ABSTRACT

The invention relates to crimson-colored pigment mixtures comprising 1,4-diketo-2,5-dihydro-3,6-diarylpyrrolo[3,4c]pyrrole and quinacridone pigments in separate crystalline phases, having a high tinctorial strength combined with other excellent application properties. The pigments according to the invention can be used in printing inks, especially in printing inks for polychromatic printed products. A substantial constituent of the pigment mixtures according to the invention is 1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole or 2,9-dichloroquinacridone, which are subjected to kneading with a crystalline inorganic salt and a neutral organic liquid. The invention also relates to a process for the preparation of such pigment compositions, the use thereof in the production of printing inks, and such printing inks themselves.

The invention relates to crimson-coloured pigment mixtures comprising1,4-diketo-2,5-dihydro-3,6-diaryl-pyrrolo[3,4c]pyrrole and quinacridonepigments in separate crystalline phases, having high tinctorial strengthcombined with other excellent application properties. The pigmentsaccording to the invention can be used in printing inks, especially inprinting inks for polychromatic printed products.

Shade, tinctorial strength, transparency and viscosity are the mostimportant parameters in printing inks. The shade must correspond to veryspecific values in order to be able to obtain together with other shadesas broad a colour range as possible, there generally being used inaddition to crimson (magenta) also blue-green (cyan), yellow and black.For that purpose the tinctorial strength and transparency should behigh, but combined with acceptably low viscosity.

EP 337 435 discloses a process for the preparation of opacifyingdiketopyrrolopyrrole pigments by wet milling in an alcohol/base system,by means of which it is also possible to treat pigment red 254.

It is known from EP 277 914 that quinacridones withdiketopyrrolo[3,4c]pyrroles in a ratio of from 5:95 to 95:5 yield solidsolutions the colour properties of which differ from those of thecomponents.

Those solid solutions are obtained by a variety of processes, includingsalt kneading in the presence of an organic solvent. The same result isalso obtained by dry milling followed by heat treatment in the presenceof a polar solvent (EP 524 904), by simultaneous decarboxylation ofsoluble derivatives (EP 654 506) and by dissolution and reprecipitationfrom basic dimethyl sulfoxide (EP 707 049), the ratio by weight of2,9-dichloroquinacridone to1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole inone Example of EP 707 049 being 3:2.

Finally, EP 737 723 discloses physical mixtures of1,4-diketo-2,5-dihydro-3,6-di(4′-bi-phenylyl)pyrrolo[3,4c]pyrrole and2,9-dichloroquinacridone that have a red shade and high opacity.

Those known products, however, have proved still to be insufficientlysuitable for printing inks, especially for inks for polychromaticprinting. The printing inks obtainable from the known pigments eitherare of an undesired shade or they are disappointing in terms of thetinctorial strength, transparency, viscosity or even several of thoseproperties simultaneously.

It has now been found that pigment compositions can be obtained that aresurprisingly more suitable for printing inks when certain1,4-diketo-2,5-dihydro-3,6-diaryl-pyrrolo[3,4c]-pyrrole and quinacridonepigments are blended under conditions such that the crystalmodifications of the components are substantially retained, that is tosay without the formation of solid solutions or mixed crystals.

It has also been found that1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]-pyrrole and2,9-dichloroquinacridone can, surprisingly, be surface-passivated bysalt kneading so that particles conditioned in that manner no longerhave a tendency to form solid solutions or mixed crystals, even whenthey are dispersed using high forces either together or with otherquinacridones or pyrrolo[3,4c]pyrroles, respectively, as is customary inthe preparation of printing inks.

The invention accordingly relates to a pigment composition comprisingpigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of the others hydrogen,chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl, C₁-C₈alkoxy orC₁-C₈alkylthio, wherein the pigments of formulae (I) and (II) have theirown separate crystalline phases and at least one pigment of formula (I)or (II) is1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo-[3,4c]pyrrole or2,9-dichloroquinacridone kneaded with a crystalline inorganic salt and aneutral organic liquid.

Separate crystalline phases are recognised by the fact that the X-raydiffraction pattern of the pigment composition corresponds to theweighted sum of the X-ray diffraction patterns of the pure components.It is probable, although unconfirmed, that the particles of differentcrystal modifications occur loosely adjacent to one another; however,aggregates of different crystal modifications likewise fully correspondto the definition according to the invention, provided they do notcontain mixed phases or solid solution regions.

The pigment of formula (I) may be a chemically uniform compound, or maybe a mixture, a solid solution or a mixed crystal of from 2 to 4compounds of formula (I). The pigment of formula (II) may be achemically uniform compound, or may be a mixture, a solid solution or amixed crystal of from 2 to 4 compounds of formula (II), which may alsocontain from 0 to 20 mol % each of the compounds of formula

and/or

Instead of pure1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole ascomponent to be kneaded, there may also be used a monophase solidsolution or a mixed crystal in which1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrroleconstitutes the host phase.

Instead of pure 2,9-dichloroquinacridone as component to be kneaded,there may also be used a monophase solid solution or a mixed crystal inwhich 2,9-dichloroquinacridone constitutes the host phase.

It is not advantageous, on the other hand, to use solid solutions ormixed crystals that comprise compounds of formulae (I) and (II)simultaneously.

When the pigments of formulae (I) and (II) are mixtures, solid solutionsor mixed crystals, preference is given to as few components of formulae(I) and/or (II) as possible, for example 2 or 3 of each, preferably 2 ofeach, which each on their own or together form a stable crystalmodification, especially physical mixtures and mixed crystals. Specialpreference is given, however, to a single compound of formula (I) or asingle compound of formula (II), and very special preference is given toonly one compound of each of formulae (I) and (II).

C₁-C₈Alkyl is, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, n-amyl, tert-amyl, n-hexyl, n-heptyl, n-octyl,2-ethylhexyl or 2,4,4-trimethyl-2-pentyl, preferably C₁-C₄alkyl,especially methyl or ethyl. C₁-C₈Alkoxy is, for example, —O—C₁-C₈alkyl,preferably —O—C₁-C₄alkyl, especially methoxy or ethoxy. C₁-C₈Alkylthiois, for example, —S—C₁-C₈alkyl, preferably —S—C₁-C₄alkyl, especiallymethylthio or ethylthio.

R₁, R₂, R₃ and R₄ are preferably chlorine, bromine, cyano, C₁-C₄alkyl ortrifluoromethyl, especially chlorine, methyl or cyano, more especiallychlorine.

The pigment of formula (I) is preferably1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)-pyrrolo[3,4c]pyrrole andthe pigment of formula (II) is quinacridone or2,9-dichloro-quinacridone, especially 2,9-dichloroquinacridone. Thepreferred pigments of formulae (I) and (II) are especially preferablycombined with one another.

The pigments of formulae (I) and (II) are known and some of them arecommercially obtainable. The ratio by weight of pigment of formula (I)to pigment of formula (II) is preferably from 1.5:1 to 1:1.2, especiallyabout 1:1.

For the kneading of the pigments of formula (I) or (II), preferably theratio by weight of crystalline inorganic salt to pigment of formula (I)or (II) is from 4:1 to 12:1, the ratio of organic liquid to crystallineinorganic salt is from 1 ml:6 g to 3 ml:7 g, and the temperature is from−20 to 100° C. The pigment particles are advantageously reduced in sizeduring kneading, with preferably a pigment of a specific surface area of≦40 m²/g, especially from 5 to 30 m²/g, being converted to a pigment ofa specific surface area of ≧40 m²/g, especially from 50 to 80 m²/g. Thespecific surface area can be determined, for example, by the nitrogenmethod.

Advantageously the crystalline inorganic salt is soluble in the neutralorganic liquid at ≦100 mg/l at 20° C., especially ≦10 mg/l at 20° C.,and is especially virtually insoluble at 20° C.

The inorganic salt and the neutral organic liquid are preferably eachsoluble in water at a concentration of at least 10 g/100 ml. Asinorganic salt preference is given to the use of aluminium sulfate,sodium sulfate, calcium chloride, potassium chloride or sodium chloride,which may optionally contain water of crystallisation. As neutralorganic liquid preference is given to the use of a mono-, bis- ortris-hydroxy-C₂-C₁₂alkane compound or a polyethylene glycol orpolypropylene glycol having from 1 to 120 ether groups, which may beunsubstituted or substituted by 1 or 2 oxo groups or at one or morehydroxy groups may be etherified by C₁-C₈alkyl or esterified byC₁-C₈alkylcarbonyl, or a mixture thereof. Examples of neutral organicliquids include C₂-C₅alcohols, such as tert-butanol,C₂-C₁₂alkylenediols, such as ethylene glycol, C₃-C₁₂alkanetriols, suchas glycerol, and diethylene glycol, or ethers thereof, such as monoglymeor diglyme, esters thereof, such as triacetin, or oxo-substitutedderivatives thereof, such as diacetone alcohol.

The temperature during kneading is preferably from 25 to 60° C. Thespeed of rotation, if appropriate taking into account cooling, should besuch that sufficient shearing occurs without the temperature exceedingthe temperature range according to the invention. Excellent results areobtained, for example, in a 5 litre kneader at speeds of 50 to 150rev/min and a kneading time of from 6 to 24 hours, but those figures arenot limiting in any way, it being possible, for example, for the speedsto be lower in larger apparatuses.

The invention relates also to a process for the preparation of a pigmentcomposition comprising pigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of the others hydrogen,chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl, C₁-C₈alkoxy orC₁-C₈alkylthio, wherein the pigments of formulae (I) and (II) have theirown separate crystalline phases, by kneading1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole aspigment of formula (I) or 2,9-dichloroquinacridone as pigment of formula(II) with a crystalline inorganic salt and a neutral organic liquid,washing out the crystalline inorganic salt and the neutral organicliquid, drying and mixing with the other component of formula (II) or(I) as the case may be. The preferred kneading conditions are givenabove. Washing out is preferably carried out with water, especiallydemineralised water. Drying is preferably carried out at from −20 to250° C./from 10⁻¹ to 10⁵ Pa, especially at from 25 to 100° C./from 10²to 10⁵ Pa or from to 200° C./from 10⁴ to 10⁵ Pa, more especially at 80°C./10⁴ Pa. Mixing can be carried out in a commercial mixer, for examplea rotary drum having mixing blades, it being advantageous to use anapparatus in which the particles are substantially not physicallyaltered. For that reason it is preferred not to use dry mills for thatpurpose or, if they are used, only under very gentle conditions.

The second component can be mixed in at any time, for example afterdrying the first component or even before washing out, in which case thekneader itself can be used as mixer.

Preferably both components of formulae (I) and (II) are kneaded,especially preferably both are kneaded according to the preferredconditions given above.

The pigment compositions obtained according to the invention aredistinguished especially by an astonishingly high tinctorial strength.They have very attractive crimson shades with excellent fastnessproperties, good transparency and good gloss. Moreover, a specific shadecan be obtained using a lower ratio of quinacridone todiketopyrrolo[3,4c]pyrrole than in solid solutions, which is veryadvantageous in view of the known very good general applicationproperties of diketopyrrolo[3,4c]pyrroles, especially in view of theirextraordinarily high chroma.

Using a nitrocellulose-based printing ink, printed by intaglio printingon standard HIFI paper (Sihl-Eica), at a total application rate afterdrying of 0.80 g/m², of which 0.06 g/m² is coloured pigment, there ispreferably obtained a hue angle h of from 350 to 360 or from 0 to 10with a chroma value C* of at least 30, especially a hue angle h of from0 to 5 with a chroma value C* of at least 33 (CIE standard 1976).

Furthermore, the surface passivation according to the inventionwithstands high compressing and shearing forces. It is accordinglysurprisingly possible to disperse the pigment compositions obtainableaccording to the invention in a ball mill or bead mill whilst retainingtheir colouristic advantages, it being especially advantageous that theviscosity of highly concentrated dispersions is also very satisfactory.

As a result of the extremely surprising advantage of much more efficientkneading, it is even possible to knead both components of formulae (I)and (II) together. As a consequence, in particular it is possible forthe kneading time required to obtain specific particle sizes andspecific surface areas to be shorter. For example, the kneading time ina 5 litre kneader at speeds of from 50 to 120 rev/min can be reduced tofrom 4 to 12 hours.

The variant of combined kneading is accordingly preferred, especially inthe case of the preferred combinations of pigments of formulae (I) and(II).

The invention accordingly relates also to a process for the preparationof a pigment composition comprising pigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of the others hydrogen,chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl, C₁-C₈alkoxy orC₁-C₈alkylthio, the pigments of formulae (I) and (II) having their ownseparate crystalline phases, by

combined kneading of1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole and apigment of formula (II) or combined kneading of 2,9-dichloroquinacridoneand a pigment of formula (I), with a crystalline inorganic salt and aneutral organic liquid,

washing out of the crystalline inorganic salt and the neutral organicliquid, and

drying.

The invention relates also to a process for the preparation of a pigmentdispersion in a ball mill or bead mill wherein pigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of the others hydrogen,chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl, C₁-C₈alkoxy orC₁-C₈alkylthio, are used, the pigments of formulae (I) and (II) havingtheir own separate crystalline phases and at least one pigment offormula (I) or (II) being1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo-[3,4c]pyrrole or2,9-dichloroquinacridone kneaded with a crystalline inorganic salt and aneutral organic liquid.

As liquid phase for the dispersion there can be used any customarydispersion medium, for example a solution of ethyl cellulose and/ornitrocellulose and/or a different known synthetic varnish in one or moresolvents, for example organic solvents, such as ethoxypropanol, ethanol,dioctyl phthalate or toluene, or water. It is also possible to usefurther additives customary for the intended application.

The preparation of pigment dispersions in a ball mill or bead mill andthe liquid phases that can be used for that purpose are very well knownto the person skilled in the art and therefore require no furtherexplanation.

The dispersions prepared according to the invention are excellentlysuitable especially as concentrates in the preparation of printing inksthat have excellent application properties, especially an attractivecrimson colour having high tinctorial strength.

The invention accordingly relates also to a printing ink or to aprinting ink concentrate comprising a pigment composition according tothe invention.

A printing ink is understood to mean a liquid or paste dispersioncomprising colourant, binder and optionally solvents and additives. In aliquid printing ink customarily the binder and optionally the additivesare dissolved in a solvent. Customary viscosities in a Brookfieldviscosimeter are from 0.1 to 20 Pa.s (spindle No. 4, 10 rev/min).Printing ink concentrates are understood to mean compositions from whichprinting inks can be obtained by dilution. Additional ingredients andmixtures of printing inks and printing ink concentrates are known to theperson skilled in the art.

The invention relates also to a printing ink comprising pigments offormulae

wherein R₁, R₂, R₃ and R₄ are each independently of the others hydrogen,chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl, C₁-C₈alkoxy orC₁-C₈alkylthio, wherein the pigments of formulae (I) and (II) have theirown separate crystalline phases, the ratio by weight of pigment offormula (I) to pigment of formula (II) is from 1.5:1 to 1:1.2 and theprinting ink, at a coloured pigment application rate of 0.06 g/m² on awhite background yields, after drying, a hue angle h of from 350 to 360or from 0 to 10 with a chroma value C* of at least 30.

The printing ink preferably comprises1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)-pyrrolo[3,4c]pyrrole aspigment of formula (I) or 2,9-dichloroquinacridone as pigment of formula(II), and especially both.

In addition to the pigments of formulae (I) and (II), and optionally(IIa) and/or (IIb), it is possible for the pigment compositions orpigment dispersions according to the invention to comprise furtherpigments, or for further pigments to be used concomitantly in theprocesses according to the invention, provided that the crystallineproperties of the pigments of formulae (I) and (II) are not therebysubstantially altered, which can be determined easily by X-raycrystallography. Additional pigments are to be understood as being anyinorganic or organic white, black or coloured pigments, with theexception of 1,4-diketo-2,5-dihydro-3,6-diarylpyrrolo[3,4c]pyrroles andquinacridones.

Additional coloured pigments in the pigment compositions or pigmentdispersions according to the invention are preferably used in smallamounts of from 0 to 20% by weight, especially from 0 to 10% by weight,based on the total weight of all the compounds of formulae (I), (II),(IIa) and (IIb). Especially preferably, however, no additional colouredpigments are used.

The printing inks according to the invention contain the compounds offormulae (I), (II), (IIa) and (IIb) advantageously in a concentration offrom 0.01 to 75% by weight, preferably from 1 to 50% by weight,especially from 5 to 40% by weight, more especially from 10 to 25% byweight, based on the total weight of the printing ink, and can be used,for example, for intaglio printing, flexographic printing, screenprinting, offset printing or continuous or dropwise inkjet printing onpaper, card, metal, wood, leather, plastics or textiles, or also inspecial applications according to generally known formulations, forexample in publishing, packaging or shipping, in logistics, advertising,in security printing or for office purposes in ballpoint pens, felt-tippens, fibre-tip pens, stamp pads, ink ribbons or inkjet printercartridges.

For intaglio or flexographic printing, it is customary to prepare aprinting ink from a printing ink concentrate by dilution, which printingink can then be used according to methods known per se. Concentratescomprising the pigment compositions according to the invention areespecially suitable.

The pigment compositions according to the invention are suitable alsofor preparing solid toners and wax transfer ribbons, as pigments incolour filters or for mass-colouring high molecular weight organicmaterials.

The high molecular weight organic material to be coloured according tothe invention may be of natural or synthetic origin and customarily hasa molecular weight in the range of from 10³ to 10⁸ g/mol. It may be, forexample, a natural resin or drying oil, rubber or casein or a modifiednatural substance, such as chlorinated rubber, an oil-modified alkydresin, viscose, a cellulose ether or ester, such as cellulose acetate,cellulose propionate, cellulose aceto-butyrate or nitrocellulose, but isespecially a completely synthetic organic polymer (thermosets andthermoplastics), as are obtained by polymerisation, polycondensation orpolyaddition, for example polyolefins, such as polyethylene,polypropylene or polyisobutylene, substituted polyolefins, such aspolymerisation products from vinyl chloride, vinyl acetate, styrene,acrylonitrile of acrylic acid and/or methacrylic acid esters orbutadiene, and copolymerisation products of the mentioned monomers,especially ABS or EVA.

From the series of the polyaddition resins and polycondensation resinsthere may be mentioned the condensation products of formaldehyde withphenols, so-called phenoplasts, and the condensation products offormaldehyde with urea, thiourea and melamine, so-called aminoplasts,the polyesters used as surface-coating resins, either saturated, such asalkyd resins, or unsaturated, such as maleic resins, and also linearpolyesters and polyamides or silicones.

The mentioned high molecular weight compounds may be present in the formof single compounds or mixtures, as plastic masses or melts, which canoptionally be spun to form fibres.

They may also be in the form of their monomers or in the polymerisedstate in dissolved form as film formers or binders for surface-coatingsor for printing inks, such as linseed oil varnish, nitrocellulose, alkydresins, melamine resins, urea-formaldehyde resins or acrylic resins.

The pigmenting of high molecular weight organic substances using thepigment compositions according to the invention is effected, forexample, by admixing such a pigment, optionally in the form of amasterbatch, with such substrates using roll mills, or mixing orgrinding apparatuses. The pigmented material is then generally broughtto its desired final form according to methods known per se, such ascalendering, compression moulding, extrusion, coating, casting orinjection-moulding. In order to produce non-rigid mouldings or to reducetheir brittleness, it is often desirable to incorporate so-calledplasticisers into the high molecular weight compounds prior to shaping.There may be used as plasticisers, for example, esters of phosphoricacid, phthalic acid or sebacic acid. In the process according to theinvention, the plasticisers can be incorporated before or after theincorporation of the pigment dye into the polymers. It is also possible,in order to obtain different hues, to add to the high molecular weightorganic materials, in addition to the pigment compositions, also fillersand/or other colour-providing constituents, such as white, coloured orblack pigments, or effect pigments, in the desired amount in each case.

For the pigmenting of surface-coatings and printing inks, the highmolecular weight organic materials and the pigment compositionsaccording to the invention are finely dispersed or dissolved, optionallytogether with additives, such as fillers, other pigments, siccatives orplasticisers, generally in an organic and/or aqueous solvent or solventmixture. It is also possible to use a procedure in which the individualcomponents are dispersed or dissolved separately or in which a pluralitythereof are dispersed or dissolved together, and only then all of thecomponents combined.

A further embodiment accordingly relates also to mass-coloured highmolecular weight organic material containing

(a) from 0.05 to 70% by weight, based on the sum of (a) and (b), of apigment composition according to the invention, and

(b) from 99.95 to 30% by weight, based on the sum of (a) and (b), of ahigh molecular weight organic material.

The high molecular weight organic material may be a ready-for-usecomposition or an article moulded therefrom, or a masterbatch, forexample in the form of granules. Where appropriate, the high molecularweight organic material coloured according to the invention may alsocomprise customary additives, for example stabilisers.

A further embodiment accordingly relates also to a method ofmass-colouring high molecular weight organic material wherein a pigmentcomposition according to the invention is used, for example by mixingand processing the high molecular weight organic material together withthe pigment composition according to the invention, optionally in theform of a masterbatch, in a manner known per se. This can be carriedout, for example, in a bead mill, an extruder or a roll mill of anydesired type of construction.

The following Examples illustrate the invention but do not limit thescope thereof (unless otherwise indicated, “%” is always % by weight):

EXAMPLE 1

A 5 litre laboratory kneader is charged with 175 g of Irgazin® DPP RedBO (Colour Index Pigment Red 254, 15 m²/g), 175 g of Cinquasia™ MagentaL RT-265-D (Colour Index Pigment Red 202, 21 m²/g), 1400 g of sodiumchloride and 350 ml of diethylene glycol and the speed is set at 50rev/min. The walls of the kneader are cooled to 25° C. so that thetemperature in the mass does not exceed 30° C. After 12 hours, 2500 mlof deionised water are added slowly, and the resulting mixture isdischarged into a Büchner funnel and washed with water until the washingwater is salt-free. The product is dried at 80° C./3×10³ Pa for 15hours.

EXAMPLE 2

A 5 litre laboratory kneader is charged with 175 g of Irgazin® DPP RedBO (Colour Index Pigment Red 254, 15 m²/g), 175 g of Cinquasia® MagentaL RT-265-D (Colour Index Pigment Red 202, 21 m²/g), 2100 g of sodiumchloride and 600 ml of diacetone alcohol and the speed is set at 80rev/min. The walls of the kneader are cooled to 25° C. so that thetemperature in the mass does not exceed 40° C. After 10 hours, 1000 mlof deionised water are added slowly, and the resulting mixture isdischarged into a Büchner funnel and washed with water until the washingwater is salt-free. The product is dried at 80° C./3×10³ Pa for 15hours.

EXAMPLE 3

A 10 litre laboratory kneader is charged with 175 g of Irgazin® DPP RedBO (Colour Index Pigment Red 254, 15 m²/g), 175 g of Cinquasia® MagentaL RT-265-D (Colour Index Pigment Red 202, 21 m²/g), 4200 g of anhydrouscalcium chloride and 2000 ml of N-methyl-pyrrolidone and the speed isset at 120 rev/min. The walls of the kneader are cooled to 25° C. sothat the temperature in the mass does not exceed 60° C. After 4 hours,5000 ml of deionised water are added slowly, and the resulting mixtureis discharged into a Büchner funnel and washed with water until thewashing water is salt-free. The product is dried at 80° C./3×10³ Pa for15 hours.

EXAMPLE 4

A 5 litre laboratory kneader is charged with 210 g of Irgazin® DPP RedBO (Colour Index Pigment Red 254, 15 m²/g), 140 g of Cinquasia® VioletNRT-201-D (Colour Index Pigment Violet 19, β modification, 70 m²/g),2100 g of sodium chloride and 600 ml of diacetone alcohol and the speedis set at 80 rev/min. The walls of the kneader are cooled to 25° C. sothat the temperature in the mass does not exceed 50° C. After 8 hours,1500 ml of deionised water are added slowly, and the resulting mixtureis discharged into a Büchner funnel and then washed with water until thewashing water is salt-free. The product is dried at 80° C./3×10³ Pa for15 hours.

EXAMPLE 5

39.60 g of nitrocellulose, 15.84 g of ethyl cellulose, 2.64 g ofmodified ketone-formaldehyde resin and 10.56 g of dioctyl phthalate aredissolved in 26.40 g of ethoxypropanol, 52.80 g of ethyl acetate and116.16 g of ethanol. 36.00 g of the product according to Example 1 arepre-dispersed therein with a high-speed stirrer at 6000 rev/min for 15minutes. The suspension is then transferred to a 125 ml bead mill with adissolver attachment (Dispermat SL™; Hediger) charged with 207 g ofzirconium ceramic beads of from 1.0 to 1.2 mm in diameter (HermannOeckel Ingenieur GmbH, D-95100 Selb). Dispersion is then carried out for15 minutes at 4000 rev/min. A ready-for-use printing ink is obtained bydilution of the resulting concentrate with a solution of 222.75 g ofnitrocellulose, 89.10 g of ethyl cellulose, 14.85 g of modifiedketone-formaldehyde resin and 59.40 g of dioctyl phthalate in 148.50 gof ethoxypropanol, 297 g of ethyl acetate and 1868.40 g of ethanol inthe high-speed stirrer for 15 minutes. Standard HIFI paper (Sihl-Eica)is printed with that printing ink using a commercial intaglio printingmachine (Rotova™; Rotocolor AG), the solids content after drying being0.80 g/m². A brilliant transparent crimson print is obtained having thefollowing colour coordinates: L*=67, C*=37, h=2.

EXAMPLE 6

The procedure is analogous to Example 5, but the product according toExample 4 is used instead of the product according to Example 1. Abrilliant transparent crimson print is obtained having the followingcolour coordinates: L*=61, C*=41, h=2.

EXAMPLES 7-8

The procedure is analogous to Example 5, but the products according toExamples 2 and 3 are used instead of the product according to Example 1.The results are virtually identical to those in Example 5 (ΔE*≦2).

EXAMPLE 9

A 0.75 litre laboratory kneader is charged with 22.5 g of Irgazin® DPPRed BO (Colour Index Pigment Red 254, 15 m²/g), 22.5 g of Cromophtal®Pink PT (Colour Index Pigment Red 122, 63.2 m²/g), 360 g of sodiumchloride and 104 ml of diacetone alcohol and the speed is set at 80rev/min. The walls of the kneader are cooled to 25° C. so that thetemperature in the mass does not exceed 40° C. After 10 hours, 150 ml ofdeionised water are added slowly, and the resulting mixture isdischarged into a Büchner funnel and washed with water until the washingwater is salt-free. The product is dried at 80° C./3×10³ Pa for 15hours.

EXAMPLE 10

A 0.75 litre laboratory kneader is charged with 27 g of Irgazin® DPP RedBO (Colour Index Pigment Red 254, 15 m²/g), 18 g of Cromophtal® Pink PT(Colour Index Pigment Red 122, 63.2 m²/g), 360 g of sodium chloride and104 ml of diacetone alcohol and the speed is set at 80 rev/min. Thewalls of the kneader are cooled to 25° C. so that the temperature in themass does not exceed 40° C. After 10 hours, 150 ml of deionised waterare added slowly, and the resulting mixture is discharged into a Büchnerfunnel and washed with water until the washing water is salt-free. Theproduct is dried at 80° C./3×10³ Pa for 15 hours.

EXAMPLES 11-12

The procedure is analogous to Example 5, but the products according toExamples 9 and 10 are used instead of the product according toExample 1. The colour results are excellent in both cases.

COMPARATIVE EXAMPLE

The procedure is analogous to Example 5, but Cinquasia® Brilliant RedRT-380-D (solid solution consisting of 40% by weight of1,4-diketo-2,5-dihydro-3,6-di-(4′-chlorophenyl)pyrrolo[3,4c]pyrrole and60% by weight of 2,9-dichloroquinacridone, 78 m²/g) is used instead ofthe product according to Example 1. The viscosity of the concentrate ina Brookfield viscosimeter using spindle no. 4 is, depending on thespeed, from 6.8 to 9.5 times higher than that of the concentrateaccording to Example 5. After 24 hours' standing time, in contrast tothe printing ink according to Example 5, very marked flocculation can beobserved. The viscosity of the printing ink in the Ford Cup No.4 is 2.2times higher than that of the printing ink according to Example 5. Witha solids content likewise adjusted to 0.80 g/m² after drying, inintaglio printing there is obtained a crimson print, the colour of whichis, however, at least 21% weaker than in Example 5. The tinctorialstrength is also at least 7% weaker than in Example 6.

What is claimed is:
 1. A pigment composition comprising pigments offormulae

wherein R₁, R₂, R₃ and R⁴ are each independently of one anotherhydrogen, chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl,C₁-C₈alkoxy or C₁-C₈alkylthio, wherein the pigments of formulae (I) and(II) have their own separate crystalline phases and at least one pigmentof formula (I) or (II) is1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo-[3,4c]pyrrole or2,9-dichloroquinacridone kneaded with a crystalline inorganic salt and aneutral organic liquid.
 2. A pigment composition according to claim 1,wherein both components of formulae (I) and (II) are kneaded.
 3. Apigment composition according to claim 1, wherein the pigment of formula(I) is1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole.
 4. Apigment composition according to claim 1, wherein the pigment of formula(II) is quinacridone or 2,9-dichloroquinacridone.
 5. A pigmentcomposition according to claim 3, wherein the pigment of formula (II) isquinacridone or 2,9-dichloroquinacridone.
 6. A pigment compositionaccording to claim 1, wherein the neutral organic liquid is a mono-,bis- or tris-hydroxy-C₂-C₁₂alkane compound or a polyethylene glycol orpolypropylene glycol having from 1 to 120 ether groups, which may beunsubstituted or substituted by 1 or 2 oxo groups or at one or morehydroxy groups may be etherified by C₁-C₈alkyl or esterified byC₁-C₈alkylcarbonyl, or a mixture thereof.
 7. A printing ink or printingink concentrate comprising a pigment composition according to claim 1.8. A mass-coloured high molecular weight organic material containing (a)from 0.05 to 70% by weight, based on the sum of (a) and (b), of apigment composition according to claim 1, and (b) from 99.95 to 30% byweight, based on the sum of (a) and (b), of a high molecular weightorganic material.
 9. A method of mass-colouring high molecular weightorganic material comprising incorporating a pigment compositionaccording to claim 1 into said high molecular weight organic material.10. A process for the preparation of a pigment composition comprisingpigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of one anotherhydrogen, chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl,C₁-C₈alkoxy or C₁-C₈alkylthio, wherein the pigments of formulae (I) and(II) have their own separate crystalline phases, by kneading1,4-diketo-2,5-dihydro-3,6di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole aspigment of formula (I) with a crystalline inorganic salt and a neutralorganic liquid, washing out the inorganic salt and the neutral organicliquid, drying and mixing with the component of formula (II) or bykneading 2,9-dichloroquinacridone as pigment of formula (II) with acrystalline inorganic salt and a neutral organic liquid, washing out theinorganic salt and the neutral organic liquid, drying and mixing withthe component of formula (I).
 11. A process for the preparation of apigment composition comprising pigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of one anotherhydrogen, chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl,C₁-C₈alkoxy or C₁-C₈alkylthio, the pigments of formulae (I) and (II)having their own separate crystalline phases, by combined kneading of1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3,4c]pyrrole and apigment of formula (II) or combined kneading of 2,9-dichloroquinacridoneand a pigment of formula (I), with a crystalline inorganic salt and aneutral organic liquid, washing out of the inorganic salt and theneutral organic liquid, and drying.
 12. A process for the preparation ofa pigment dispersion in a ball mill or bead mill wherein pigments offormulae

wherein R₁, R₂, R₃ and R₄ are each independently of one anotherhydrogen, chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl,C₁-C₈alkoxy or C₁-C₈alkylthio, are used, the pigments of formulae (I)and (II) having their own separate crystalline phases and at least onepigment of formula (I) or (II) being1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo-[3,4c]pyrrole or2,9-dichloroquinacridone kneaded with a crystalline inorganic salt and aneutral organic liquid.
 13. A process according to claim 10, 11 or 12,wherein the specific surface area of the pigment during kneading isincreased from ≦40 m²/g to ≧40 m²/g.
 14. A process according to claim10, 11 or 12, wherein the temperature during kneading is from −20 to100° C.
 15. A process according to claim 10, wherein both components offormulae (I) and (II) are kneaded.
 16. A process according to claim 10,wherein the pigment of formula (I) is1,4-diketo-2,5-dihydro-3,6-di(4′-chlorophenyl)pyrrolo[3 ,4c]pyrrole. 17.A process according to claim 10, wherein the pigment of formula (II) isquinacridone or 2,9-dichloroquinacridone.
 18. A process according toclaim 10, herein the specific surface area during kneading is increasedfrom ≦40 m²/g to ≧40 m²/g.
 19. A process according to claim 16, whereinthe pigment of formula (II) is quinacridone or 2,9-dichloroquinacridone.20. A printing ink comprising pigments of formulae

wherein R₁, R₂, R₃ and R₄ are each independently of one anotherhydrogen, chlorine, bromine, cyano, trifluoromethyl, C₁-C₈alkyl,C₁-C₈alkoxy or C₁-C₈alkylthio, wherein the pigments of formulae (I) and(II) have their own separate crystalline phases, the ratio by weight ofpigment of formula (I) to pigment of formula (II) is from 1.5:1 to 1:1.2and the printing ink at a coloured pigment application rate of 0.06 g/m²on a white background yields, after drying, a hue angle h of from 350 to360 or from 0 to 10 with a chroma value C* of at least 30.